Ground engaging tools (GET), for earth-moving equipment, such as those used in mining operations, operate in a highly abrasive environment and are subject to significant wear. GET such as bucket teeth thus require regular replacement.
Traditionally, GET are welded onto the lips of buckets. When the GET come to the end of their useful life, they can be cut from the bucket, and new GET welded in their place.
It will be appreciated that such cutting and re-welding operations are complex, time-consuming and relatively expensive. Further, they must generally be done in a workshop, requiring the bucket to be transported away from the earth-moving equipment.
Various mechanical attachment methods have been proposed in an attempt to alleviate these problems. Many of the methods involve the use of bolts and similar fastening devices, inserted within the lip of the bucket. In general, such devices have proved to be of limited use. The insertion of a bolt or similar within a bucket lip can lead to undesirable stress concentrations within the lip, resulting in cracking of the bucket lip. Even where this is avoided, the large forces to which GET are exposed have a tendency to deform connecting bolts, thus making difficult their subsequent extraction using mechanical tools. Indeed, in some cases the deformation can be so severe that the GET must be cut away, completely negating any advantage of mechanical connection.
In response to these issues, the applicant has devised a number of mechanical connection means which overcome these problems. Examples of the applicant's devices are detailed in U.S. Pat. No. 7,219,454 and in U.S. patent application Ser. No. 10/509,016, the contents of which are included herein by reference.
These connection means involve the use of a shroud which mounts about a lug or boss on the lip of an excavator bucket; a locking device which locates between the shroud and the boss; and the application of an external compressing force to maintain the relative position of the shroud, locking device and boss.
Although these connection means have proved far less susceptible to deformation than previous mechanical connectors, there have nonetheless been occasions where the connection means have failed due to a load being applied which is higher than the means can bear. Where the external compressing force has been applied by a threaded element, such as that described in U.S. application Ser. No. 10/509,016, one mode of failure observed has been the deformation of the mating threads between the force applying element and the locking device.
When such a failure occurs, the force applying element (a bolt) seizes within the locking device. It can then be difficult or impossible to remove the bolt using normal mechanical tools.
Depending on the relative hardness of the bolt and the locking device, deformation of the threads of either can occur. In either case, the result can be seizure of the locking device.
The present invention seeks to provide a means by which such seizure of the locking devices can be substantially avoided.